The present invention relates to a femoral hip prosthesis, and more particularly to a femoral hip stem component.
Hip arthroplasty procedure includes anesthesia and patient placement on a table in proper orientation. The patient's body is then stabilized, scrubbed, prepared and draped. An incision is made and the subcutaneous tissue is divided. Appropriate soft tissue is excised and/or divided for exposure and dislocation of the hip. After the femoral head is dislocated from its associated acetabulum, the head is rotated for better exposure. A femoral neck osteotomy is then performed wherein the head and neck are cut away from the femur shaft. Next, the intermedullary canal is prepared to accommodate the hip stem component of the prosthesis and, ultimately, the stem is anchored within the intermedullary canal.
Prior to the present invention, numerous femoral inserts have been proposed for use in hip joint prostheses. Generally, each includes a polished spherical head or capitulum mounted upon a stem, which is inserted into the intermedullary canal of the femur. Often, the inserts are cemented within the canal to hold them fast against the applied forces and loads. Such inserts are described, for example, in U.S. Pat. Nos. 3,102,536, 3,320,951, 3,818,512, 3,874,003, 3,875,593, 3,965,490, 4,012,796 and 4,080,666.
The characteristics of the spacing or interface between the exterior surface of the femoral stem and the interior contour of the prepared cavity in the intermedullary canal play an important role in properly anchoring the insert to the femoral bone. A stem of sufficient length has long been recognized as desirable since it provides increased surface area for cementing within the canal and increased resistance to rotation. However, long stems require large intermedullary cavities, particularly at the calcar leading into the canal, since the overall surface thereof makes it impossible for the insert to pass into the canal without a significantly oversized entranceway. Such cavities result in large gaps or voids between the outside surface of the inserted stem and the inside surface of the cavity. Heretofore, a glove fit between a femoral stem and the intermedullary cavity together with superior anchoring of the stem and resistance to rotation have been considered difficult to achieve.